1. Field of the invention
The present invention relates to a method for manufacturing integral elastic supports and to an integral support obtained by means of this method.
Typical examples of elastic supports manufactured according to the present invention are the backs and seats for contoured chairs or wheelchairs, for the physically challenged and older people, supports for parts of the bodies of patients forced to long periods of immobility, seats for industrial vehicles, and saddles for bicycles and motorcycles.
2. Description of the Prior Art
It is known that the region of contact between the surface of the support and the part of the human body that must be supported is normally concentrated proximate to the ischial bones of the pelvis. Accordingly, specific pressure is relatively high in these regions and can prevent oxygenation of tissues and correct blood circulation, causing so-called bedsores and other similar disorders. In other cases, as in bicycle saddles used by healthy individuals and athletes, the high specific pressure can create extremely troublesome irritations or affections of the tissues and can, in some cases, temporarily or permanently damage delicate organs, such as the gertitalia and the prostate. On this subject, reference is made to the article published by "Bicycling" magazine of July 1993, pages 57-60. These effects are sometimes increased by the presence of discontinuities or folds on the covering of the support, caused by lack of tension or of adhesion of the covering to the underlying filler.
In order to reduce the specific pressure in the above mentioned delicate regions of the body, supports have been produced that are formed by an outer covering that encloses a padding which includes one or more layers or sacs of materials that are more resilient than the rest of the support. The materials used for this purpose are gaseous, such as compressed gas or air, particularly flexible elastomeric materials, open-cell polyurethane foams, some high-viscosity oily or thixotropic liquids, or combinations of these materials. Examples of these supports are given by French patent No. 2,306,866, by German patent No. 75,799, by European patent No. 0 013 527 and by U.S. Pat. Nos. 718,850, 3,161,436, 4,012,072, 3,807,793, 4,588,229, and 4,808,469.
Supporting structures with elastomeric materials In gel form that behave like liquids but have partial resilience or elastic memory have recently been perfected; reference is made to U.S. Pat. Nos. 3,548,420 and 3,663,973 on this subject.
These known supporting structures generally include a layer of gel material formed by a composition of siloxane or organosiloxane polymers, as disclosed by U.S. Pat. No. 3,020,260. In all these known applications, the gel material has no shape of its own and must therefore be enclosed within impermeable walls or appropriate containers made of flexible material. After being enclosed, the gel can be integrated in a filler made of foamed elastomeric material.
The bicycle saddle structure produced in accor-dance with U.S. Pat. No. 4,815,361 in the name of Chiarella has a supporting frame made of nylon, polypropylene or other relatively rigid plastic material; a layer of foamed elastomeric material, for example polyurethane foam, obtained separately by molding in a closed mold so that it has a recess that corresponds to the ischial region in its central part is glued onto the frame. The recess is meant to accommodate a sac of organosiloxane gel material, also as disclosed by U.S. Pat. No. 3,020,260. These three parts are mutually superimposed, and a covering of flexible material, for example Lycra or fabric, is applied on them, stretched and anchored to the lower edges of the frame. This saddle and the associated manufacturing method have numerous disadvantages, mainly linked to the use of the particular organosiloxane gel. Since this material does not have a shape of its own, it must in fact, be contained laterally by the lateral edges of the cavity formed on the upper part of the polyurethane foam filler. The filler must therefore be shaped separately arid allowed t,o cure completely in order contain the gel insert downward and laterally. Furthermore, since the silicone gel is unstable, i.e. has a limited shelf life and breaks down easily if it, is subjected to repeated and rather intense stresses, releasing highly impregnating polyhydric alcohols, it must be carefully isolated within a sealed sac made of impermeable material of a certain thickness, for example polyethylene, to avoid leaks or impregnation of the covering. Consequently, the covering cannot be placed directly in contact with the gel compound but must be protected by an intermediate layer that unavoidably reduces the elastic fluid-mechanical properties of the compound. Generally, the saddle manufacturing method according to U.S. Pat. No. 4,815,361 requires an excessive use of labor, with considerable finished-product costs. The method for stretching the support covering layer also does not ensure a uniform supporting surface that is free from creases or discontinuities that reduce the final quality of the finished support and are poorly accepted by users.
The aim of the present invention is to provide an integral elastic support that includes an insert made of gel material that can be obtained by means of an extremely simple and repetitive method, with a very limited use of labor, and can thus be automated substantially completely, so as to considerably reduce production costs and times.
An object is to provide an integral elastic support that includes a gel insert or layer that maximally exploits the hydroelasticity properties of this material.
Another object is to provide a discontinuous process for the mass-production of integral gel supports that are substantially free from discontinuities and surface creases and have a high quality level.